When watching any of the Star Trek series or movies, we sometimes see scenes in orbit around alien planets. I am always amazed at the creativity of the artists who create these environments, building worlds that are clearly elsewhere but yet have many features that remind us of our world. Clouds, for example.
We are of course familiar with the various cloud features of our planet Earth, and we have seen images from space probes and telescopes of clouds on some of the other worlds of our Solar System, such as Venus, Mars, the giant planets, and even one of the moons, Titan. What do these clouds tell us? Here on Earth they can mean rain, storms, or simply a bit of cover from the sun during the summer. On Venus, they cause the runaway greenhouse effect, that gives Venus a surface of over 700 degrees (F). On Mars, they look mostly whispy in the thin atmosphere. And on Saturn’s moon Titan they hide an very cold surface with liquid methane.
Jupiter’s (left) and Neptune’s (right) cloud features. Credit: NASA.
Our giant planets all have their own cloud features, from Jupiter's Great Red Spot to Neptune’s dark blue and white clouds. While the atmospheres of the giant planets are leftovers from the solar nebula from which our Solar System formed, those of the terrestrial planets formed from outgassing of volcanoes, and in case of Earth, later from the photosynthesis of the emerging plant life. Of course, much later the industrialization of our civilization added another component, which will most certainly be detectable if someone should guess what to look for.
Would the planets around other stars also have clouds? There is no reason to assume they they wouldn’t. As astronomical instrumentation continues to advance, we are able to detect more and more details about these exoplanets, including, for the first time, cloud features in the atmosphere.
In cooperation between the Kepler Space Telescope and the Spitzer Space Telescope, it was possible for the science teams to map cloud features on this planet named Kepler-7b.
Kepler 7b (left), which is 1.5 times the radius of Jupiter (right), is the first exoplanet to have its clouds mapped. The cloud map was produced using data from NASA's Kepler and Spitzer Space Telescopes. Credit: NASA/JPL-Caltech/MIT.
This world is about half again as large as our Jupiter, but has an orbit of only five days, so it is closer to its primary star than our Mercury (which has a period of 88 days), and therefore is very hot. It is one of the new planetary categories called “hot Jupiters”. A planet this close to its sun should be much hotter than it actually is, however, the clouds appear to have a cooling effect on this planet. It is still quite hot though, about 1600 degrees (F) or so. The clouds appear not be uniformly distributed, they are much thicker on one side of the planet than on the other.
While we may be disappointed that this is not an Earth-sized world with nice fluffy (or stormy) water clouds, it is the very first time we are able to see cloud features on a distant world. Kepler 7b is about 1000 light years away from us, so what we are seeing today actually happened there 1000 years ago. If someone from that neighborhood was looking at Earth right now, they would see us as Earth was during the time of the Middle Ages in Europe, the Song Dynasty in China, and the Toltec civilization in Central America.
As our ability to detect and monitor alien worlds advances, we will be able to see such cloud features on smaller worlds as well. Sadly, the Kepler Space Telescope has recently experienced failures of two of its four gyros, rendering it unable to continue the search for extrasolar planets as before. It will perform other astronomical observations, but the precision pointing required for planet hunting is unfortunately no longer possible. Hopefully there will be a successor for this spacecraft, allowing us to resume our quest for alien worlds.
Here are a few links if you’d like to know more about this topic:
MIT News “Scientists generate first map of clouds on an exoplanet“:
JPL News “NASA Space Telescopes Find Patchy Clouds on Exotic World”:
Ex Astris Scientia: